Page 790 - Veterinary Toxicology, Basic and Clinical Principles, 3rd Edition

Botulinum Neurotoxins Chapter | 55 749

VetBooks.ir 30,000 IU. One dose typically provides coverage for should be monitored frequently to determine the need for
artificial ventilation. Intranasal oxygen insufflation and
about 60 days (Sprayberry and Carlson, 1997; Whitlock
mechanical ventilation can be instituted in foals with poor
and Buckley, 1997). The use of parasympathomimetics
should be avoided because these agents deplete acetylcho- arterial blood gas values and/or metabolic acidosis.
line stores and exacerbate paresis/paralysis. Antibiotic Unfortunately, mechanical ventilation is not practical in
therapy is indicated in cases of wound botulism or sec- the adult horse (Mitten et al., 1994).
ondary infections; however, aminoglycosides, tetracy- A more optimistic prognosis is associated with low
cline, procaine penicillin, and metronidazole are doses, slow disease progression, and mild clinical signs.
contraindicated. Aminoglycosides block neurotransmis- A poor prognosis is associated with rapid disease onset
sion at the neuromuscular junction and will exacerbate with recumbency after 8 12 h. A positive response to
muscle weakness and paralysis (Barsanti, 1990). antitoxin therapy is indicated by the ability to eat rela-
Although gram-positive anaerobes are sensitive to penicil- tively normally within 7 10 days posttreatment and
lin and metronidazole, administration of these drugs is regain full strength within a month. The most common
controversial. These antimicrobials may cause more bac- complications associated with botulism are decubital
terial lysis, thus increasing the release of toxin (in the ulcers and aspiration pneumonia; these problems can be
case of a toxicoinfection), or they may promote C. botuli- resolved with supportive care and antimicrobial therapy.
num colonization by altering the normal intestinal flora.
Drugs such as the aminopyridines and guanidines should Prevention
also be avoided because they will further deplete acetyl-
choline stores (Critchley, 1991). Following recommended vaccination protocols, basic
After antitoxin administration, supportive care is the wound hygiene, and sound husbandry methods reduces
mainstay of treatment. H 2 blockers and proton pump inhi- the occurrence of equine botulism. Forages should be
bitors may be indicated, especially for foals. Topical oph- examined for carrion, and pastures should be cleared of
decaying vegetation and rotting animal carcasses. To
thalmic ointments should be used to prevent corneal
date, only serotype B toxoid vaccine is marketed for
abrasions and ulceration. Adult horses may require seda-
horses in the United States. In general, vaccination is only
tion with xylazine or diazepam to reduce anxiety and
recommended for horses in endemic areas. Adult horses
exertion. Patients should be muzzled between feedings to
in endemic areas should be vaccinated annually. Mares
reduce the risk of aspiration pneumonia. Nutritional sup-
should be boosted 4 6 weeks prior to parturition to
port should be provided to dysphagic patients. Alfalfa
slurries with adequate amounts of water may be adminis- achieve adequate antitoxin immunoglobulin (Ig) levels in
tered through a nasogastric tube to adult horses. Foals colostrum. Foals born to vaccinated mares should receive
should receive milk replacer through a nasogastric tube or a series of three vaccinations, each 1 month apart, starting
parenteral nutrition if ileus is present. Patients should be at 2 or 3 months of age. Foals born to unvaccinated mares
maintained in sternal recumbency to prevent aspiration should be vaccinated at 2, 4, and 8 weeks of age
pneumonia and checked periodically for gastric reflux (Whitlock and Buckley, 1997; Galey, 2001).
because ileus may lead to the accumulation of ingesta/
fluid in the stomach. If gastric reflux is not present, some Bovine Botulism
authors recommend that mineral oil be administered via a
nasogastric tube to alleviate ileus and constipation; how- Cattle are susceptible to botulinum toxins B, C1, and D,
ever, this should be done under close supervision due to and the most common form of the disease is caused by
the increased risk of aspiration in these patients. ingestion of preformed toxin in spoiled silage, carrion-
Recumbent patients should be turned frequently or sus- laden silage (typically serotype B), or silage contaminated
pended periodically by full-body slings to prevent decubi- with poultry litter (typically serotype C1 and more rarely
tal ulcer formation, myopathies, and other complications D; Divers et al., 1986; Heider et al., 2001; Galey et al.,
of prolonged recumbency. Recumbent stallions and geld- 2000; Braun et al., 2005; Martin, 2003; McLoughin et al.,
ings should be catheterized twice daily to empty the blad- 1988). Pica associated chewing on bones and carrion in
der and prevent pressure necrosis or cystitis (Whitlock area with phosphorus deficient soils and/or protein defi-
and Buckley, 1997). ciencies is a noted risk factor, particularly for toxin sero-
A tracheostomy should be performed in cases of botu- type D. Carcasses of animals that have died from
lism in which horses show signs of upper airway obstruc- botulism present an ongoing risk to other animals under
tion as a result of paralysis of the nares or larynx. In more such circumstances. Transfer of carrion by foxes and
complicated cases, patients may require intravenous fluids crows has been reported overseas as an indirect method of
to correct respiratory acidosis resulting from decreased disease spread. Outbreaks of botulism in feedlots (and
ventilation. For foals in particular, arterial blood gases other intensive animal production systems) have been